Hi Kingpin,
If you use a quad LM324 or dual LM358 for the DC fine and course frequency control buffers, then their high noise level might cause the project's frequency to twitch. Certainly not for the output buffer, since they were designed for very low power (in their day) and therefore have lousy high frequency response. It will give hardly any output at 100kHz and just about nuthin' at 1MHz. I don't know about any other good buffer than the one shown. :lol: